Update 3-31-16: event now live in Europe and Australia.
Update 3-31-16 #2: Jirachi is now available in North America!
As a part of the Pokémon 20th anniversary celebration, Jirachi will be given away via WiFi to owners of Pokémon X, Y, Omega Ruby, and Alpha Sapphire starting this Friday.
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Got it already, but I guess another wouldn't hurt.